Conventional imaging radar requires the control of transmitted and/or received wavefronts (beamforming). In particular, target detection systems as used in military and commercial applications require accurate beam steering of transmitted signals to detect and identify targets.
In an analogous application, detection of the presence of insects, such as termites, in a structure requires accurate signal transmission and processing. Australian Patent AU 693039 assigned to the present applicant, describes a system for detecting the presence of insects in a structure by transmitting a microwave signal into a wall. Any disturbances in the received signal are detected and processed to indicate the presence or otherwise of insects.
The above system however, is not able to determine the number, species and activity of the insects. Control and processing of the field pattern of the antenna is required to accurately determine the presence, location and type of activity of insects.
Typically, in most conventional applications, far field beam steering is performed. It is also possible to control the transmitted near field pattern of a transmit antenna. However, this is expensive and difficult to do, as it is necessary to control the magnitude and phase of the carrier signal to each transmitter array element. Typically PIN diode phase shifters and attenuators are used. Phase control and magnitude control is poor, even with three bits of phase control, which is already difficult to achieve. Illumination control of the transmitted near field pattern in general is ineffective when transmitting into an inhomogeneous structure such as a wall in a house.